I am using HPLC/MS to determine the concentration
of a compond in urine and want use creatinine to nomalize. I know there are some kits to determine the consentration of creatinine in urine. But I am not sure these kits are suitable for my purpose. I think the situation is popular. All your advice and sugesstions will be appreciated.

We used an automated system for creatinine determinations for a number of years. Our agricultural studies, while examining normal work conditions, exposed the farm workers to the extremes of temperature, and thus hydration and creatinine concentrations. It was close to worst-case situations, and we felt we needed creatinine correction values.

Eventually our toxicologists realized that creatinine corrections, because of the dynamic nature of metabolism, were not worth the trouble. There is so much variability in the samples and the analyses over the period of time we measured--a few days from exposure--that the minor corrections didn't really do much. Your time is probably better spent collecting and running additional real samples.

Of course, your situation may be different. You will need to evaluate the repeatability and accuracy of the 'test kits' you would like to use, in order to determine if they will serve your purpose. Our analysis was extremely reproducible, and also accurate.

You might be able to make an arrangement with a medical lab for such a simple analysis, since they do them all the time.

I would suggest plugging some extreme values, and also numbers representing normal values, into some of your existing data, and then re-evaluate that data, being sure to look at the BIG PICTURE. This would show you what would happen. While corrections may change each individual value, it probably won't change the overall evaluation very much.

Good Luck, and a good question! Put that computer to work for something besides the Internet.